Calculate top distance (status bar height and navigation bar height) of UIViewController without use UIApplication.shared

Usually when i develop iOS application, i need to calculate the top distance of UIViewController, this distance is sum of statusbar height and navigationbar height, the simple code you can use to do this is:

/// Get distance from top, based on status bar and navigation
public var topDistance : CGFloat{
     get{
         if self.navigationController != nil &&!self.navigationController!.navigationBar.isTranslucent{
             return 0
         }else{
            let barHeight=self.navigationController?.navigationBar.frame.height ?? 0
            let statusBarHeight = UIApplication.shared.isStatusBarHidden ? CGFloat(0) : UIApplication.shared.statusBarFrame.height
            return barHeight + statusBarHeight
         }
     }
}

If we have to use a code inside an app extension, we have this error during compile process:

“‘shared” is unavailable: Use view controller based solutions where appropriate instead

The only way to avoid this error is to calculate distance without use: UIApplication.shared, the simple idea is to add a subview in a UIViewController, constraint it to navigation bar if present and calculate the height difference, here a simple code:

extension UIViewController{
    
    
    /// Calculate top distance with "navigationBar" and "statusBar" by adding a
    /// subview constraint to navigationBar or to topAnchor or superview
    /// - Returns: The real distance between topViewController and Bottom navigationBar
    func calculateTopDistance() -> CGFloat{
        
        /// Create view for misure
        let misureView : UIView     = UIView()
        misureView.backgroundColor  = .clear
        view.addSubview(misureView)
        
        /// Add needed constraint
        misureView.translatesAutoresizingMaskIntoConstraints                    = false
        misureView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive     = true
        misureView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive   = true
        misureView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
        if let nav = navigationController {
            misureView.topAnchor.constraint(equalTo: nav.navigationBar.bottomAnchor).isActive = true
        }else{
            misureView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
        }
        
        /// Force layout
        view.layoutIfNeeded()
        
        /// Calculate distance
        let distance = view.frame.size.height - misureView.frame.size.height
        
        /// Remove from superview
        misureView.removeFromSuperview()
        
        return distance
        
    }
    
}

You can use it after view has been loaded, with this code:

class myClass : UIViewController{
override func viewDidAppear(_ animated: Bool) {
      print(self.calculateTopDistance())     
   }
}